1. Field of the Invention
The present invention generally relates to storage devices, and more specifically, to a storage device having a latch mechanism configured to latch an unloaded head in a structure where the head can be loaded or unloaded against a recording medium.
2. Description of the Related Art
In a magnetic disk apparatus having a ramp mechanism, a magnetic head is loaded on a magnetic disk from a parking position of the ramp mechanism via a ramp. The magnetic head on the magnetic disk is unloaded to the parking position via the ramp of the ramp mechanism. The magnetic head situated on the parking position is latched to the parking position by a latch mechanism formed by a magnet or the like so that the magnetic head is prevented from moving on the ramp or the magnetic disk carelessly.
Therefore, at the time of unloading, it is necessary to control the head moving mechanism so that the magnetic head is driven from the parking position by an unlatch force sufficient for unlatching.
In a conventional magnetic disk apparatus, an operation for unlatching the magnetic head at the time of loading is done by a closed-loop control so that a constant driving electrical current is applied to the head moving mechanism. While there is variation in the latch force for every magnetic disk apparatus due to bad parts, bad installation of the ramp, or the like, the magnetic head can be securely unlatched by applying a driving electrical current, sufficient for unlatching the magnetic head, to the head moving mechanism.
A method for detecting a moving speed of a magnetic head from a VCM (Voice Coil Motor) back electromotive voltage and a method for switching the moving speed of the magnetic head depending on a position of the magnetic head on the ramp mechanism are disclosed in U.S. Pat. No. 6,754,027. Furthermore, a method for reducing the influence on a head speed signal detected from the VCM back electromotive voltage of mutual interference noise from peripheral circuit sections is disclosed in U.S. Pat. No. 6,754,027. In addition, a magnetic disk device capable of stably controlling magnetic head speed even when frictional force changes suddenly at the time of getting on and off a ramp due to variation in coil resistance of a VCM in loading/unloading operations of the magnetic head is disclosed in U.S. Pat. No. 6,496,319. Furthermore, a method for reading a load profile from a ROM so as to update it for a load profile peculiar to a magnetic disk apparatus is disclosed in U.S. Pat. No. 6,212,027.
However, if an excessive driving electrical current, which applies an unlatch force larger than necessary as compared to the latch force applied by the latch mechanism to the magnetic head, is applied to the head moving mechanism of the magnetic head, the ramp may be worn down due to drastic movement of the magnetic head so that fine particles may be generated, the magnetic head may be damaged due to an insufficient floating amount of the magnetic head above the ramp, or a large mechanical noise may be generated when the magnetic head is moved.
In addition, in the conventional magnetic disk apparatus, the latch force of the latch mechanism configured to latch the magnetic head is not measured. Therefore, even if a magnetic disk apparatus has a latch mechanism whose actual latch force is smaller than a designed value due to bad parts or bad installation, the magnetic disk apparatus may be shipped.
Because of this, in the magnetic disk apparatus whose latch force is smaller than the designed value, when an impact is received from the outside, the magnetic head may be unlatched on the ramp or the magnetic head may move onto the magnetic disk. This may cause the magnetic head to become adhered on the magnetic disk in a case where the magnetic disk is not being rotated.
In addition, in a magnetic disk apparatus whose latch force is smaller than the designed value, if a driving electrical current is applied whose value is sufficient for unlatching a magnetic head in a case where the latch force has the designated value, as discussed above, excessive driving electrical current may be applied to the head moving mechanism.
In other words, in the conventional art, a driving electrical current proper for unlatching the magnetic head cannot be applied to the head moving mechanism for every magnetic driving apparatus. Furthermore, it is not possible to identify storage devices having a latch mechanism whose latch force is smaller than a designed value at the time when the storage devices are shipped.